Device for etching rinsing and drying substrates in an ultra-clean atmosphere

ABSTRACT

An etching, rinsing and drying device for substrates ( 7 ) comprises a tank ( 5 ) having a diffusing bottom ( 9 ) and an overflow chute ( 2 ). Projection nozzles ( 10, 11 ) are arranged in the diffusing bottom ( 9 ) so as to inject an etching liquid LG and a rinsing liquid LR into the tank. The tank ( 5 ) is equipped at the top part with at least one injection manifold ( 1 ) of a drying liquid LS to form a superficial layer of uniform thickness above the water constituting the rinsing liquid LR. The drying liquid LS is immiscible in water and presents a lower surface tension and density than those of water.

BACKGROUND OF THE INVENTION

The invention relates to a tank enabling the stages of etching, rinsing and drying of substrates requiring ultra-cleanness to be performed successively without the substrates having to be moved throughout running of the different stages of the process, and enabling the liquids used for each of the etching and drying stages to be recovered in order to recycle and filter them for re-use, thus reducing the consumption thereof.

STATE OF THE ART

The successive stages of etching, cleaning, rinsing and drying are currently performed in independent tanks requiring the basket containing the substrates to be transferred from one piece of equipment to the other. Thus, the document FR-A1-2,797,405 describes an ultra-clean rinsing tank comprising a rinsing liquid diffusing device and an overflow chute. The rinsing tank also comprises rinsing liquid projection nozzles connected to feed systems and a deflector designed to divert the rising flows of the rinsing liquid. This type of tank does not however enable the substrates to be etched or dried.

In certain cases, removing the substrates from the bath between the stages preceding drying is not possible, as this results in destruction of the structures. This is the case of certain micro-system structures (MEMS, MEOMS, etc . . . ). For this type of substrate, alternative solutions exist based on successive dilution of the etching liquid by the rinsing liquid, then by one or more liquids presenting an increasingly lower surface tension and soluble with one another, before the substrates are removed from the bath. This method presents the drawback of requiring a large volume of the liquids used for etching, rinsing and drying without it being possible to recycle these liquids. Thus, the document EP-A1-1,158,257 describes a method and device for washing and drying substrates. The device comprises a tank in which substrates are placed to then be successively washed and dried with washing and drying fluids. Drying of the substrates is performed using the Marangoni effect based on creation of a surface tension gradient The Marangoni effect does however require the two fluids to be miscible with one another.

OBJECT OF THE INVENTION

The object of the invention is to achieve a tank enabling the etching, cleaning, rinsing and drying stages to be performed successively or independently using ultra dean fluids, and enabling the fluids used for etching and drying to be recovered so as to separate them from the rinsing water and to filter them in order to be able to recycle them, thus enabling their consumption to be reduced.

The etching, rinsing and drying device for substrates according to the invention comprises:

-   -   a tank having a diffusing bottom at the bottom part and an         overflow chute at the top part,     -   projection nozzles arranged in the diffusing bottom and         connected to independent feed systems for injection of an         etching liquid and a rinsing liquid,     -   at least one deflector situated in proximity to the overflow         chute to divert the rising flows of liquid,     -   means for circulation of the different liquids in the tank,     -   and an injection manifold for injecting a drying liquid to form         a superficial layer of uniform thickness above the water         constituting the rinsing liquid, said drying liquid being         immiscible in water and presenting a lower surface tension and         density than those of water.

The drying liquid can be constituted by isopropanol accompanied by additives, or isopentane, or any other liquid substance immiscible with water.

Other features can be used either alone or in combination:

-   -   the overflow chute is equipped with a series of orifices and         recovery valves specific to each of the etching, rinsing and         drying liquids;     -   an independent reprocessing circuit for the etching, rinsing and         drying liquids is used for purification and filtration of the         products for recycling of the latter;     -   means reverse the flow due to the hydraulic piston effect         generated by the feed system of the bottom connected to the         nozzle system in the central position, so as to expel the liquid         in the ascending direction to the overflow chute and to perform         replacement of this liquid by an identical liquid in the case of         several cycles when the etching and rinsing stage is performed,         or by a different liquid in the case of replacement of the         liquid between the etching, cleaning and rinsing stages;     -   the use of the hydraulic piston effect also enables the drying         liquid to be recovered after the basket has been removed, by         removing the liquid from the tank via the overflow chute;     -   drying of the substrates is performed by passing the basket         containing the substrates through the layer of drying liquid         after drainage of the bath has been performed;     -   according to an alternative embodiment, drying of the substrates         is performed by removing the basket upwards making the         substrates pass through the superficial layer of drying liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a front cross-section view of the tank containing a substrate basket during the process.

FIG. 2 is a side cross-section view of the tank of FIG. 1 after the substrate basket has been removed.

FIG. 3 represents a perspective top view of the tank illustrating the drying liquid injection and distribution system, the overflow chute, and the end of the three recovery systems with their valves.

FIG. 4 shows a perspective bottom view of the tank enabling the liquid recovery system and the etching and rinsing liquid feed system to be seen.

FIGS. 6 to 9 illustrate the successive etching and rinsing stages.

FIGS. 10 to 13 show the drying stages.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

With reference to FIGS. 1 to 4, the tank (5) comprises at its base an ultra-clean liquid diffusing device (9), whereto two feed systems (12 and 13) are connected at the bottom part enabling etching and rinsing liquids to be injected to the central nozzles (10) and lateral nozzles (11). The central feed system (12) is connected to the first nozzle system (10) arranged in the central part, and the peripheral feed system (13) is connected to the second lateral nozzle system (11).

The two nozzle systems, central system (10) and lateral system (11), are integrated in the diffusing bottom (9). The enclosure of the tank (5) is connected at the bottom part to the part containing the diffusing device (9). The top part of the enclosure of the tank (5), in the lateral position, is composed of deflectors (4) enabling the flow from the lateral nozzles (11) to be diverted, thus creating circulation of the liquid inside the tank (5) and generating a downward flow of the liquid in proximity to the substrates (7).

Two basket supports (8) are securedly affixed to the piece (9) constituting the diffusing device to guarantee the central position and the stability of the basket (6) containing the substrates (7). The top part of the tank enclosure (3) is constituted by an overflow (3) formed by crenellated parts to ensure a homogeneous overflow of the liquid into an overflow chute (2).

The overflow chute (2) enables the excess water to be recovered during the rinsing phase, and the etching, rinsing and drying liquids to be recovered for reprocessing at the end of each processing phase. At the bottom of the overflow chute (2) there is provided an outlet orifice (15) enabling the different liquids to be recovered. This outlet orifice (15) is connected to three independent recovery systems for the liquid used for etching, rinsing and drying.

Each recovery system is formed by a pipe (16, 19 and 22), an opening and closing valve (17, 20 and 23) and a connector (18, 21, 24) enabling the liquid reprocessing systems to be connected. The pipes (16 and 19) for the etching and drying liquid present a raised part with respect to the lowest level in order to prevent undesirable liquid from being recovered, i.e. recovery of the etching liquid by the circuit reserved for the drying liquid, and vice-versa.

Two tubes (1) enabling the drying liquid to be inlet to the surface of the bath are fixed to the external walls of the overflow chute (2). These tubes (1) are placed in parallel manner above the overflow (3) on two opposite sides. They are formed by a plurality of orifices (25) arranged at regular intervals over the length corresponding to that of the tank (5), thus achieving a uniform distribution of the drying liquid over the whole surface of the bath. These two tubes (1) are connected to a common drying liquid distribution system (14). The positioning of these tubes (1) enables both the basket (6) containing the substrates (7) to be inserted, and the drying liquid to be injected inside the tank (5) only, and not into the overflow chute (2).

A draining system (27) of the tank (5) is connected by means of a T-shaped junction to the feed pipe of the first, central, nozzle system 10. An adjustable valve (26) enables the draining rate of the tank (5) to be controlled.

When operating in the etching stage, as represented schematically in FIG. 6, the tank (5) is first filled with an etching solution, notably hydrofluoric acid, the dilution whereof determines the etching rate. The etching time is determined by the thickness of oxide to be etched and the dilution of the etching solution.

The basket (6) containing the substrates (7) previously prepared for etching is inserted in the tank (5) filled with etching liquid LG by means of a robotized arm (not shown in the figures). The basket (6) is held in position by means of basket supports (8) supported by the bottom of the tank. The volume of etching liquid LG previously injected into the tank (5) is controlled so that insertion of the basket (8) does not cause the tank to overflow, in order to minimize the quantity of liquid to be recycled.

The substrates (7) can be made of silicon, quartz, ceramic, or be metallic or oxide-based.

In FIG. 7, etching of the substrates (7) is performed either with a static bath or with a dynamic bath presenting a circulation. In the latter case, an injection system of the etching liquid LG via the lateral nozzles (11) is provided. The etching liquid LG thus injected can come from the etching liquid reprocessing system.

In FIG. 8, etching is stopped by replacing the etching liquid LG by the rinsing liquid LR, in particular de-ionized water, by means of the hydraulic piston effect exerted in the upwards direction. This circulation takes place following injection of the rinsing liquid LR by means of the central nozzle system (10 and 12), able to be accompanied or not by circulation of the same liquid by the lateral nozzle system (11 and 13).

The hydraulic piston effect enables the etching liquid LG to be replaced without being mixed with the rinsing liquid LR. Recovery of the etching liquid LG is performed by the overflow chute (2) in which the outlet orifice (15) connected to the recovery system (15, 16, 19 and 22) is arranged. Opening of the corresponding valve (17, 20 and 23) enables the recovered liquid to be sent to a reprocessing system of the etching liquid LG. Control of the liquid flows through the two nozzle systems enables total control of the liquid flows in the tank (5), and therefore enables the mechanical stresses applied in the proximity of the surface of the substrates due to the hydrodynamic flow to be controlled.

At this stage of the process, the substrates (7) have been etched, and etching has been stopped by the de-ionized rinsing water. The substrates (7) remain immersed in the deionized water bath throughout the rinsing operation (FIG. 9).

The rinsing stage of the substrates (7) is performed in similar manner to that described in the document FR 2,797,405. Circulation of the de-ionized water enables an upward flow to be generated parallel to the surface of the substrates (7) due to the lateral nozzle system (11). This circulation enables the efficiency of the rinsing to be increased and therefore enables the rinsing process time and the quantity of water required to be reduced.

At the end of the rinsing operation, replacement of the rinsing water by clean de-ionized water is performed by hydraulic piston effect as described above. These two operations (rinsing water circulation and replacement of the latter by piston effect) are repeated several times until the optimum rinsing level is obtained. An equivalent quantity in volume of dirty water corresponding to that injected by the lateral nozzle system (11) is recovered by the overflow chute (2). All of the water flows in the overflow chute (2) so as to be recovered for recycling by the corresponding system (15, 22, 23 and 24).

After the rinsing stage described above, the drying stage illustrated in FIGS. 10 to 13 is performed.

With reference to FIG. 10, a small quantity of water is drained off from the tank (5) in order to reduce the level below the overflow chute (3), without a part of the substrates (7) emerging from the upper surface of the water. Draining is performed by the central nozzles (10) and the central pipe (12) to which the T-shaped junction and valve (26) are fixed. A junction connects the valve (26) to the water recycling circuit (27).

When the water level is sufficiently low, the drying liquid LS is inlet to the surface of the bath by means of the nozzles (25) provided in the tube (1). The drying liquid LS presents a lower density and surface tension than the de-ionized water, and is not miscible with water.

For example, the drying liquid LS constituting the superficial layer can be isopropanol accompanied by additives, or isopentane, or any other liquid immiscible with water. The surface tension values are the following:

-   -   for water: 73.05 10⁻³ N.m⁻¹ for a temperature of 18° C.;     -   for isopropanol: 21.7 10⁻³ N.m⁻¹ for a temperature of 20° C.;     -   for isopentane: 13.72 10⁻³ N.m⁻¹ for a temperature of 20° C.

The drying liquid LS can also come from condensation of a gas at the surface of the water.

Consequently, a layer formed by the drying liquid LS forms at the surface of the bath. The thickness of this layer LS is controlled by the quantity of liquid injected. Drying of the substrates (7) is performed by passing the basket (6) containing the substrates through this layer of drying liquid. To do this, draining of the bath is performed so that the whole surface of the substrates (7) passes through the drying liquid LS (FIG. 12). Drainage is performed at a relatively low and regular rate so that the action of replacing the water by the drying liquid can take place completely on the geometries that may be present at the surface of the substrates.

Another possibility consists in removing the basket (6) upwards (FIG. 11) making the substrates (7) pass through the superficial layer of the drying liquid LS.

Control of the drainage rate is performed by means of the adjustable valve (26, FIG. 2). A siphon is placed after the drainage valve (26) to guarantee that bubbles do not rise up into the tank (5) when drainage takes place. Drainage is stopped once all of the substrates (7) have been removed from the bath, but before the layer formed by the drying liquid at the surface of the de-ionized water bath reaches the bottom (9) of the tank.

The substrates (7) are then dry. The basket (6) is removed from the tank (5) by a robotized arm. The drying liquid LS can then be recovered. To do this (FIG. 13), the tank (5) is again filled with water injected through the central nozzles (10) and lateral nozzles (11) using the hydraulic piston effect until the whole of the layer of drying liquid LS that was at the surface of the bath passes into the overflow chute (2).

The water and drying liquid mixture is then recovered by the corresponding piping system (15, 22, 23 and 24) and sent to the corresponding reprocessing circuit for separation of the drying liquid LS and water, followed by reprocessing for re-use.

To revert to the initial situation, drainage of the water is performed via the pipe (12) with recovery of the water (26 and 27), followed by filling of the tank (5) with the etching liquid.

The field of application of the invention covers any type of flat substrates requiring ultra-clean etching, rinsing and drying processes, in particular substrates that present micronic or sub-micronic structures of “floating structure” type at their surface. What is meant by floating structure is any structure having bonding dimensions to the substrate that are much smaller than the dimensions of the structure itself. These floating structures are sensitive to mechanical stresses in the course of wet processes, and also to the stresses generated by capillary forces after they have been released by etching. These stresses are in particular molecular breaking and binding of the surfaces of these floating structures.

The field of application concerns:

-   -   micro-technology substrates: MEMS (micro-electronic mechanical         systems), MEOMS (micro-electronic & optical mechanical systems)         and micro-mechanisms;     -   micro-electronics substrates;     -   substrates used for fabrication of bio-sensors;     -   substrates used in optronics;     -   substrates used for fabrication of flat panel and liquid crystal         displays. 

1-10. (Canceled)
 11. Etching, rinsing and drying device for substrates comprising: a tank having a bottom part and a top part with a diffusing bottom at the bottom part and an overflow chute at the top part, projection nozzles arranged in the diffusing bottom and connected to independent feed systems for injection of an etching liquid LG and a rinsing liquid LR, at least one deflector situated in proximity of the overflow chute to divert rising flows of liquid, and means for circulation of the different liquids in the tank, wherein the tank is equipped at the top part with at least one injection manifold for injecting a drying liquid LS to form a superficial layer of uniform thickness above the water constituting the rinsing liquid LR, said drying liquid LS being immiscible in water and presenting a lower surface tension and density than those of water.
 12. Etching, rinsing and drying device according to claim 11, wherein the etching liquid LG is constituted by hydrofluoric acid.
 13. Etching, rinsing and drying device according to claim 11, wherein the drying liquid LG is constituted by isopentane.
 14. Etching, rinsing and drying device according to claim 11, wherein the overflow chute is equipped with a series of orifices and recovery valves specific to each of the etching LG, rinsing LR and drying LS liquids.
 15. Etching, rinsing and drying device according to claim 11, wherein it comprises a reprocessing circuit for the etching liquid LG, rinsing liquid LR and drying liquid LS, enabling the liquids to be purified and filtered for recycling.
 16. Etching, rinsing and drying device according to claim 11, wherein it comprises means for reversing the flow due to an hydraulic piston effect generated by the feed system of the bottom connected to the nozzle system in central position, so as to expel the liquid in the ascending direction to the overflow chute and to perform replacement of this liquid by an identical liquid in the case of several cycles when the etching and rinsing stage is performed, or by a different liquid in the case of replacement of the liquid between the etching, cleaning and rinsing stages.
 17. Etching, rinsing and drying device according to claim 11, wherein it comprises a common drainage system of the liquid contained in the tank, and means enabling the drainage rate to be controlled.
 18. Etching, rinsing and drying device according to claim 11, wherein drying of the substrates is performed by passing a basket containing the substrates through a layer of drying liquid LS after drainage of the liquids contained in the tank has been performed.
 19. Etching, rinsing and drying device according to claim 11, wherein drying of the substrates is performed by removing a basket upwards making the substrates pass through the superficial layer of drying liquid LS.
 20. Etching, rinsing and drying device according to claim 11, wherein the substrates housed in a basket remain permanently in a liquid medium, as they are immersed in the etching liquid LG until the end of the drying state. 